I agree with the links suggested by JimP. The thing is, the space after is controlled by tab settings in the Style as well as Indent settings in the numbering. When the number (or bullet) takes up space beyond the tab setting, you will get your problem.
If you need more on Styles, look at my page:
Understanding Styles in Microsoft Word. It is much longer, has lots of links, and is not as well-organized because it has been being added to over a 17-year period. I think that learning to utilize styles is THE key to having Word work for you, or at least with you.